A user roaming in an area covered by several telecommunication networks may choose an operator, a RAT (Radio Access Technology), and/or a frequency of communication based on roaming agreements between operators in this area and on the capabilities and preferences of its User Equipment (UE).
Cognitive Pilot Channel (CPC) is a kind of Beacon channel that may be used in cognitive radio to provide information to cognitive mobiles about the available operators, Radio Access Technologies (RAT's) and Frequencies available in the geographical area.
The CPC is used to support a terminal during the “start-up” phase and “on-going” phase:                During the start-up phase, beginning, at “switch on” of the mobile terminal, the mobile terminal is searching for a candidate network to camp on; and        In the “on-going” phase, the mobile terminal is camping on a network with a dedicated RAT and is able to listen to CPC message broadcasted through the network in order to rapidly detect changes in the environment due to either variation of the mobile position or network reconfigurations.        
From this two mobile state, different CPC deployment approaches are possible:                In the out-band CPC solution, where the CPC is conceived as a radio channel outside the component Radio Access Technologies, the CPC either uses a new radio interface, or alternatively uses an adaptation of legacy technology with appropriate characteristics; and        In the in-band CPC solution, the CPC is conceived as a logical channel within the technologies of the heterogeneous radio environment.        
For both deployments, a CPC manager broadcasts CPC information continuously and periodically for all mobiles presents in the CPC area.
Two major concepts for Cognitive Pilot Channel are proposed by the E3 project and ETSI RRS Group in order to organize RAT's information according to a geographical area: Mesh based approach and Coverage area approach.                In Mesh based concept, a geographical area covered by a beacon channel, is divided into a plurality of zones, called meshes and information is provided about operators RAT and frequencies available in each mesh.        In Coverage area concept, information about all the RAT's and frequencies available with respective RAT's coverage area in the area covered by a beacon channel is broadcasted in the geographical area.        
FIG. 1 illustrates a geographical area 2 divided in different zones 4, each zone being covered by a network base station 6 using a Radio Access Technology (RAT) and receiving Beacon services from a Beacon base station 8.
In Mesh based concept, CPC information represents a large quantity of data to be sent especially if the mesh size is small. This forces mobile phones roaming in area 2 to listen to CPC channel longer than coverage area approach. It is to be noted that CPC information are updated according to the network load (new frequencies available or not) and network structure update (new technology, new frequencies, new operator). The frequency update is low between several posts of CPC message, therefore a mobile phone will receive several time the same information.
One of the proposed methods to reduce the CPC data rate is to transmit one CPC message for the whole CPC area, not to meshes of the CPC area, and transmit the coverage area for each technology and frequency. The problem with this kind of approach is that coverage areas are not easily characterized and transmitting a detailed coverage area may result in a large data-rate as well.